The ability of Peyer's patch cell to present antigens of varying chemical composition is under investigation. The adherent cells from Peyer's patches (APPC) have been isolated and found to contain Ia antigens and yet do not present soluble antigen to sensitize T cells from syngeneic animals. The relationship between the ability of APCC to present antigens and the capacity of these antigens to induce systemic tolerance when given orally is under study. With some antigens, such as soluble, proteins systemic tolerance when given orally is under study. With some antigens, such as soluble, proteins systemic tolerance can be induced and antigen specific splenic suppressor cells are found on adoptive transfer. Systemic tolerance is accompanied by an active secretory response to the specific antigen. Whether suppressor cells and/or soluble circulating factors are involved in tolerance to particulate (bacterial, cellular) antigens is currently under study.